3C295 in Context
3C295 is enveloped by a vast cloud of fifty million degree gas.
The gas cloud, which is visible only with an X-ray telescope,
contains more than a hundred galaxies and enough material to
make a thousand more. The galaxies in most cases do not contain
enough hot gas to be observed with an X-ray telescope, but they
do show up in optical photographs. Because the galaxies were
discovered before the hot gas cloud, these objects are called
galaxy clusters, or clusters of galaxies.
Palomar Observatory image made
by R. Minkowski in 1960, giving the optical
identification of the central galaxy in the cluster
3C295. Angular size of box = 15 arc min.
Galaxy clusters are formed through the merger of smaller groups
and clusters over billions of years. The gas in clusters is
thought to have been heated to fifty million degrees or more
when the cloud collapsed about five to ten billion years ago.
Galaxy clusters are the most massive gravitationally bound
objects in the universe.
In recent years X-ray observations have shown that galaxy
clusters must contain large amounts of dark matter to hold the
hot gas cloud together. The total mass of the dark matter needed
is typically about five times as great as the mass of the gas
and the galaxies. Chandra observations may provide insight into
what constitutes dark matter and how it is distributed.
X-ray image of 3C295
The gas in the central regions of the 3C295 cluster shows signs
that it is cooling and settling onto the central galaxy.
Astronomers think that the material falling onto 3C295 over the
eons has caused it to grow into its present size and shape. It
contains several times the mass of our Milky Way galaxy and
resembles a giant glowing basketball.
The explosion that wracked 3C295 about a million years ago and
produced the X-ray knots and radio lobes was probably due to the
infall of gas onto the galaxy. In much the same way that a
torrent of water pouring down a drain can produce a back
pressure if the flow is more than the drain can handle, the
enormous energy released by too much matter flowing into a
supermassive black hole could trigger an explosion. Great
quantities of matter and energy would be hurled back into the
surrounding gas cloud, in a powerful payback for eons of being
dumped on by a cosmic bully.
X-ray-radio composite of
NASA/CXC/SAO/NRAO/AUI/NSF/R.Perley & G.
Return to 3C295 (16 Nov 99)